Gold sulfite baths containing organophosphorus compounds

ABSTRACT

Disclosed is an improved gold-sulfite bath for plating gold and gold alloy deposits. By the inclusion in the bath of small amounts of certain organic phosphorus compounds, the quality of the deposit is rendered less sensitive to substantial changes in operating variables.

United States Patent Losi et al. Sept. 9, 1975 [54] GOLD SULFITE BATHS CONTAINING 3,475,292 10/ 1969 Shoushanian 204/44 ORGANOPHOSPHORUS COMPOUNDS 3,666,640 5/ 1972 Smith 204/ 44 3,672,969 6/1972 Nobel et al. 204/43 G [75] Invent rs: vat r s Geneva, Switzerland; 3,770,596 1 1973 Bick et al 204/43 0 Pierre Lalanne, Gex, France; Rene Henzi; Erwin Marka, both of OTHER PUBLICATIONS Geneva, Switzerland [73] Assignee: Oxy Metal Industries Corporation, 223 2 x fg z Nature Detroit, Mich.

[22] Filed: Aug 8, 1973 Harold Narcus, Metal Finishing, Vol. 50, No. 3, pp.

5462, (1952). [21] Appl. N0.: 386,798

Primary Examiner-G. L. Kaplan [301 Forelgn Apphcatlon Pflorny Data Attorney, Agent, or Firm-Arthur E. Kluegel; Richard Aug. 10, l972 Switzerland 11975/72 P Muellgr; B, F, Claeboe Aug. 6, 1973 Switzerland ll388/73 [52] US. Cl 1. 204/43 G; 204/46 G; 260/5024- R;

260/5024 P; 260/5024 A; 260/5025; [57] ABSTRACT [51] nt Cl 2 czsn jlg g Disclosed is an improved gold-sulfite hath for plating F Id 204 43G 44 46 G gold and gold alloy deposits. By the inclusion in the [58] o earc bath of small amounts of certain organic phosphorus 6 compounds, the quality of the deposit is rendered less [5 1 References cued sensitive to substantial changes in operating variables.

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a P/V g ra ao sum 6 BF 7 GOLD SULFITE BATHS CONTAINING ORGANOPHOSPHORUS COMPOUNDS The present invention concerns the use of organophosphorus compounds in sulfite baths for the electrodeposition of gold and gold alloys as additives for improving the performances and theoperating conditions of said baths.

The invention also concerns the sulfite baths for the electrodeposition of gold and gold alloys which contain at least one of said organophosphorus compounds.

The invention also concerns the process of depositing coatings of gold and gold alloys the electrolysis of gold and gold alloys sulfite baths containing said organophosphorus compounds.

In general, these organophosphorus additives will often, relatively slight variations of current density result in the formation of foggy deposits,nburns, pittings or colour changes, particularly when depositing gold alloys.

The introduction of said phosphorus compounds .into sulfite gold baths largely prevents these diffieultiesaln the presence of such additives, it is possible to vary operational factors between relatively wide limits without affecting the quality of the coatings and, in case of gold alloys, without appreciably modifying the composition and the carat thereof. The principle of action of these additives is not known exactly; it is however possible that they may standardize the'electrochemical properties of the various metals which are plated simultaneously, e.g. the electrodeposition potential and the distribution of ions in the cathode layer.

I The present additives are stable water-soluble organic compounds of phosphorusof valency fouror five comprising at least one P atom having up to four bonds identical or different chosen among PR and POR and having connected to the possibly free remaining valencies thereof substituents selected among 0 and OH free or salified with alkali metals, NHf, earth-alkali metals or the metals which participate to the electrodeposition of the gold and its alloys.

The groups indicated by symbol R, identical or different, comprise monovalent or divalent organic radicals. In said second alternative, they can either be connected together in cyclic form or bridge with at least another phosphorus atom. R can denote the following substituents v l. A linear, branched or cyclic aliphatic radical saturated or not which may comprise at least one func tion selected among halogens, CN, NH- CO, OH, COOH and SO H free, as salts as mentioned above or esterified.

2. A monoor polycyclic aromatic radical which can be substituted by linear, branched or cyclic aliphatic groups and which can comprise, as well as the substituent groups, at least one function like (1 above.

3. A radical as under l above further comprising at least one aromatic or heterocyclic substituent containing at least one N, O or S, said substituents themselves comprising or not functions as under l above.

4. Aradical as under (1), (2) or (3) above which is interrupted by at least one N or O atom, the third valency of the N atom being connected to a hydrogen atom or to an organic rest.

5. A radical as described under (1) to (4) which is connected to a tetravalent P atom and a function of which having a labile proton is under anionic form to balance with the positive cationic charge of the phosphorus atom.

The number of carbon atoms of each substituent R is preferably comprised between I and 30 although this number can be exceeded in some cases.

Hence, among the compounds useful according to the present invention the following can be found a. Quaternary phosphonium compounds R P X X being an anion derived from an organic or inor ganic acid or an anionic function of one of the R groups (X can be derived for instance from H 50 HCl', CH COOH, CI COOH, etc.).

b. Phosphine oxides R PO.

c. Phosphonic acids RPO(OH)- free, monoor diesterified.

d. Ph'osphinic acids R PO(OH) free or esterified.

e. Organic phosphates ROPO(OH) (RO) PO(OH) and (ROMPO.

Naturally, compounds will also be found which are similar to the above but which have some of their substituents R connected to at least one second P atom substituted symmetrically or not symmetrically with the first one.

The phosphorus compounds which are preferably used as additives in sulfite baths for the electrodeposition of gold and gold alloys are phosphonic acids, phosphinic acids or mixed phosphono-phosphinic acids, their salts and their ester derivatives. Consequently, they can comprise one or seeral phosphorus atoms and the acid functions thereof can be free, salified or esterified partially or completely. It has been found that in many cases phosphoric and phosphonic esters are as active or more active than the correspnding free acids when added to the present gold baths and this observation is very surprising and completely unexpected. Indeed, if, as it is generaly supposed, the activity of the free acid additives is due to the affinity between the acid OH functions and the metal ions dissolved in the bath, it is difficult to understand how the ester functions which should be relatively inert can even be more active. It should also be noted that the halogen and carbonyl derivatives of the present organo-phosphorus compounds are particularly active.

The present additives can be classified in a more de- 6 tailed manner as follows 1. Compounds containing one phosphonic groups of formula wherein A represents a linear, branched or cycle containing alkyl or aralkyl hydrocarbon chain saturated or not comprising from 1 to 30 C atoms some of which may be substituted with one or several substituents. selected among OH, CN, halogens (Cl, Br or I), COOH or SO H groups free, salified or esterified, NRR groups and oxygen (carbonyl groups). In addition, chain A may have inserted in the main part thereof or in the side branches one or several hetero-functions, e.g. O and NR. R and R are selected among hydrogen and linear or branched alkyl radicals halogenated or not having I to 6 C atoms, e.g. CH C H C H iso- C H CICH CICH CHCI, (CICH )2CH, etc., CH COOH and CH SO H free, salified or esterified. Furthermore, R and R can constitute together with the N atom a 5 to 6 links heterocycle. R has the same meaning as R or R but also comprises alkylene bridges connected to a possible second N atom of A.

2. Compounds having at least two phosphonic groups of formula HO) POB-PO(OH (2) wherein B represents a C,to C linear, branched or cycle containing alkylene or aralkylene hydrocarbon chain saturated or unsaturated which may be substituted with one or several substituents selected among OH, CN, halogens (Cl, Bror I), acid groups such as COOH, S0,,H or PO,,H free, salified or esterified, NRR groups and oxygen (carbonyl groups). In addition, chain B can be interrupted or not by one or several hetero-functions, egv O and NR. R and R represent the same substituents as R and R but further comprise a (CH ),,,PO H group free, salified or esterified (m l or 2). R comprises the same substituents as R and. in addition, a CH PO H group free, salified or esterified.

3) Compounds having at least two phosphonic groups of formula wherein R represents a halogen (Cl, Br or I) or an OH (free or etherified); R" represents H, halogens or C to C linear or branched alkyl or alkenyl groups which may be substituted or unsubstituted by at least one group selected among OH, CN, halogens (Cl, Br or 1),

acid groups such as COOH, SO -,H and PO H free. salified or esterified and oxygen.

4. Phosphinic and phosphono-phosphinic compounds of formulae similar to (l), (2) and (3) above but wherein the OH function of at least one of the phosphorus atoms is replaced by a group A the definition of which is the same as for A above. Thus, examples of formulae of type (4) will be as follows:

wherein A, B. R and R are defined as above and A is preferably a linear or branched alkyl radical which may or not be substitued by halogens (Cl, Br or I), OH or NRR R' and R being defined as above.

5. Phosphono-phosphinic compounds of formula similar to (2) above wherein chain B is interrupted by one or several HOPO groups.

In the above compounds the ester and ether functions are preferably derived from lower alkanols which may be halogenated or not, e. g. methanol, ethanol, propanol, isopropanol, butanol, isobutanol, CICH OH, Cl CHOI-I, ClCH --ClCHOH, (ClCH -CHOH, etc.

A number of organophosphorus compounds which are useful according to the invention are listed below as non limitative examples. In the formulae of these compoundsthe acid functions have been generally represented in the free state but it is understood that such functions can actually be salified or esterified as mentioned above. This list of compounds which is far from being exhaustive is followed by references relative thereto, e.g. to the preparation thereof. Some of these references also comprise other compounds which can be used according to the invention and which are in accord with formulae, l) to (5) above. Generally, when the present compounds were initially obtained as esters, the latter were hydrolized by usual means, e. g. by I boiling with aqueous mineral acid or alkali. However, in some cases, for instance with compounds having a P-CO bond some breakage of that bond occurred during hydrolysis, in which case the ester was preferably used as an additive in gold electroplating baths. Free acidic functions were esterified by usual means, e.g. by boiling with an alcohol in the presence or in the absence of a catalyst such as H HCl, BF etc.

Since the following list of compounds is not exhaus-' tive, it will be understood that analog. homolog and other compounds similar to those outlined can also be useful according to the present invention.

Compounds of formula l CA. 68, 24798; 68, 6882; 68, 95891; 67, 73652; 67, 43887; 67, 11549; 52, 241b; 50, 3993; 52, 7127d; 50, 11230g; 50, 10760g; 52, 3667; 51, 10366h.

South-Africa Patent No 6804,07].

US. Pat. Nos. 3,309,342; 3,322,863; 3,314,957;

French Patents Nos 1,458,492; 1,458,566;

Dutch Patents or published Patent Applications Nos German Patents or published Patent Applications Nos 1,232,142; 1,943,577; 1,194,852; 1,235,836.

Belgian Patents No 672,205; 619,619.

British Patents Nos 941,706; 703,180; 703,381;

Sulfite baths for the electrodeposition of gold and gold alloys in which the present additives are particularly useful are known from the men skilled in the art. Such baths are described for instance in Swiss Patent No 506,628 and British Patent No 1,134,615. These baths contain the gold as a sulfite of gold or a gold sulfite complexed with an amine, the concentration of which can vary, for instance, from 0.5 to 30 g of metal /I. They generally contain alkali or ammonium sulfites the quantity of which can vary from 1 to 150 g/l, chelateing or complexing agents such as water-soluble organic acids and hydroxyacids, e.g. citric, lactic, gluconic, tartaric, malic and acetic acids, corresponding alkali or ammonium salts and dior polyamines. A series of such amines can be found for instance in Modem Coordination Chemistry by J. LEWIS & R. G. WILKINS, Intersc. Publ., New York, page xiii and comprises for instance ethylene diamine (en), ethylene diamine tetraacetic acid (EDTA) and diethylenetriamine pentaacetic acid and their alkali and ammonium salts. The amount of said additives is not critical and essentially depends on the bath compositions and the particular use thereof. Generally, concentrations between 0.1 g and 100 g/l of such ingredients are possible. These baths can also contain various metal ions operating as brightening agents, e.g. Ni, As, Sb and Se, or

being codeposited in larger amounts with the gold to form gold alloys. As such metals, the following ones can be mentioned Fe, Co, Ni, Zn, Cd, Sn, Cu, Bi, Ga, In, Pb, Mn, Mo, Ag, Tl, Zr, V, W and, in some cases, the precious metals of the platinum group. Said metal ions are introduced into the present baths as watersoluble salts, chelates or complexes well known in the electroplating art (see for example The Metal Finishing Guidebook Directory, Metals and Plastics Publ., Inc., Westwood, N..I., U.S.A.). The sulfates, sulfites, citrates or carbonates of said metals, complexed or not with the above described complexing agents, are used preferably when soluble in water. The amount of said metals in the present baths can vary between wide limits depending on the composition and the carat of the alloys to be plated. It can be comprised, for instance, between 0.5 and 150 g/l. However, these limits are not critical and it is possible to have concentrations below or above said limits in some cases. Thus, when the metals are used only as brightening agents, very small quantities can be effective, e.g. in the order of only 1 to 500 mg/l.

The present bathscan also contain mineral or or ganic acids and bases as well as buffers so that the pH can be maintained between operating limits according to usual means. Examples of such acids are H HCl, H SO HCOOI-I and others. Examples of such bases are NaOI-I, KOH, LiOH and others. Examples of such buffers are citrate, borate and phthalate buffers. The pH of said baths are generally comprised between about 5 and l 1; however, a given bath may have rather narrow operative pH limits.

The sulfite baths for the electrodeposition of gold and gold alloys operate at current densities generally comprised between rather' narrow limits. For instance, in the case of a typical sulfite gold-copper bath, the optimal current density at C is about 1 A/dm in such case, it is not advisable to operate at densities 20 more or less than the average value as defective coatings might be produced (burns or alloy composition variations).

In contrast, in the presence of some of the additives used according to the invention, it is possible to operate at i 50 76, or better, of the medium density value without changes in the aspect and the properties of the deposited alloy. In some favourable cases, this interval, can be even wider. Therefore, the importance of other operating factors closely related to the bath conductivity and consequently to current density are strongly minimized, e.g. temperature, pH, concentration of conductivity improving agents, type and strength of agitation, distance between anodes and the parts to be plated, etc. Generally, the addition of these organophosphorus compounds into the present baths permits obtaining deposits having reproducible and constant properties even in the case of relatively important variations in the operation parameters.

The effective quantities of the compounds useful according to the invention can vary between wide limits. These quantities depend, naturally, on the chemical structure of the phosphorus compound considered, that is on the nature and the number of the functional groups and, presumably, on their orientation. In some cases, a few mg/l, e.g. I to 2 mg/l are sufficient; in other cases higher concentrations, e.g. of the order of 10 to g/l or even up to the limit of solubility in the bath can be desirable and advantageous.

The present additives can be incorporated to the baths, depending on the case, as the pure substances or a ready prepared solutions in water or water-soluble liquids such as alcohol, acetone or others.

When the non esterified forms of the present additives are used, it is generally immaterial that they should be added into the baths as the free acids or as the alkali salts thereof with the condition, of course, that the final pH of the bath be adjusted to the required value with an acid or a base, e.g. H 80 or NaOI-I.

Table 1 below shows the composition of a few sulfite gold and gold alloy baths wherein the present organophosphorus additives are very useful.

TABLE 1 GOLD AND GOLD ALLOYS SULFITE BATHS Concentrations in g/l; concentrations of the alloy metals in g of metal /l orgachelatant Current nic alkali Rochelle of type pH density Ex. Au Cd Ni Zn Cu Sb acid sulfite salt en EDTA 1C A/dm A) 10 20 50 10 50* 60 6.5-6.8 60 (ms-i .2 B) 8-35 4 40 10 9.540 58 1.5 C) 8-30 0.1 0.3-1 20-50 I00 20 80* 2-5 7.07.5 65 0.8l .0 D) 3-10 l5 6 I00 E) 3-8 17 5-10 0.2 100 F) 6 l 2 5 I00 G) 6 l2 5 0.05 I00 The above haths further contain 0.2 to 5 g/l of one or several of the following ingredients:

- saturated or unsaturated higher organic monoor polyacids. egv sehacic, stearic. linolcic. etc. organic compound having at least one trivalent nitrogen atom. e.g. nicotinic acid. dipyridyl.

- wetting agents of the alkyl or aryl-sulfonate type. l auryl sodium sulfate. FCGB***, etc. optionally. 0.0] to 5 g/l of the following metal ions: Pb. Fe, Se. Hg Cs. Pd. As, Sh. In. Co.

Au is present as gold sulfitc or gold sulfite complexed with an amine. e.g. en.

Cu. Cd. Ni, Zn. Sb are present as water-soluble compounds (mineral or organic acid salts. complex salts. e.g. with en) on ethylene diamine. ED'IA ethylene diamine tetraacctic acid tetrztsodium salt; disodium salt.

EXAMPLES l to 18 A sulfite bath for the electrodeposition of an Au-Cu- Cd alloy having a white to yellow-white colour was pre pared by mixing the following ingredients at the concentrations indicated. EDTA means ethylene diamine tetraacetic acid or the alkali salts thereof.

Ingredients Concentration Au (as gold sulfite) 6 g/l Cd (as EDTA complcxed sulfate) 12 g/l Ni (as EDTA complexed sulfate) 3 g/l Cu (as EDTA complcxed sulfate) 0.06 g/l EDTA (free) g/l N21 80 30 g/l pH (NaOH) 9,7 10

crating conditions could be varied only very slightly without experiencing difficulties. Indeed, when the current density was increased 0.] or 0.2 A/dm (that is up to 0.6 or 0.7 A/dm the platings started to burn. In addition, the levelling action was poor. that is the action of hiding originally produced defects (e.g. burns) by the freshly deposited layers of alloy: for instance, it was noted that when burns were intentionally produced by increasing the current density and thereafter the current was reduced to normal (0.5 A/dm the bums remained present even at much higher coating thickness. It should also be noted that operating the above bath below 0.5 A/dm may be inconvenient as the colour of the deposit becomes yellower.

Aliquots of the above control bath were taken and modified by adding in each 0.005 to 0.01 mole/l of one of the organo-phosphorus additives shown in Table 2 below. Then the above plating operations were repeated with each of the modified baths.

The differences resulting from the presence of the additive on the quality of the platings and on the operating conditions were recorded. The main parameters which were checked were the levelling power defined as above, the surface condition of the deposit (gloss) and the limits of variations of the current density during plating without producing defective coatings.

The results obtained (Examples of compounds 1 to 18) plus control are recorded in Table 2 which also shows the concentration of each of the additives used. The composition of the plated alloy was about l819 carat 20 Cd and 23 Cu).

H l l 2 TABLE 2 CURRENT EXAMPLE ORGANO-PHOSPHORUS CONC. DENSITY SURFACE LEVELLlNG A DDlTlVE No. g/l INTERVAL CONDITION ACTION 1 (HO) OPCOH-PO(OH). ;6 2 l excellent excellent H O I 2 (CH O OP-COHCH Cl l E 1 excellent excellent CH. 3 (HO OPCOHCH CI 0.) "=l good good 3 4 (HO OPCHCl- 0.8 E good acceptable 5 (CH O OPCOC H 0. 8 E good acceptable 6 [(HO OP] CH 0.9 1 good good 7 [(HO .,oP-cH. 1 2 2 good good 8 (C H O) OP-CH l .5 good good 9 (HO OP(CH. );,PO( OH l good good 10 HO ,OP-CH C0OH 0.7 E acceptable acceptable 1 1 NaO PQCH O 1.6 E l acceptable good .H,-,c. .o 2 l 2 OH H -,C O POCPO( OC- .H l .8 2 12-0 2 acceptable inferior (C H OH l3 (H C O POCO( CH ):OH 1 (1.2-0. 3 inferior inferior l4 (H,,C O POCONHC.,H. l 3 0.2 acceptable inferior l5 (HO) PO(CHOH CH OH l 5 0.2-0 3 acceptable inferior l6 HO OPCO PO( OH l 5 excellent excellent 17 HO OPCCl PO( OH l l 5 excellent excellent 1 x H,,c. .o OH

PO C 2 1 .5-2 excellent excellent HO CH Control 0. 1 poor none As can be seen from the results of Table 2, some of the additives are more active than others. However, it does not appear to be any correlation of the activity with the chemical structure.

The quantities of the additives used in the Examples shown in Table 2 are quite small, however the amount of some of them can be further decreased without decreasing too much their effect. If the concentration of said additives is increased in the plating baths, their action will be still augmented up to a maximum of efficiency. The concentrations corresponding to this maximum depend strongly on the kind of the additive and on the composition of the bath wherein it is used. In general, because of cost considerations, it is advantageous to operate at concentrations in the neighbourhood of those indicated in Table 2.

The organo-phosphorus additives used in Examples 1 to 18 can be prepared as follows (the temperatures are in degrees Centigrades).

l. Diphosphono-ethyl-hydroxy-methane 1hydroxypropane-l l -diphosphonic acid Ref.: Belgian Patent No. 619.619. A mixture of 164 g (2 mole) of orthophosphorus acid (14 1 and 260 g (2.2 mole) of propionic anhydride was heated to 160C for 2 hrs. Then the mixture was steam distilled until the condensed distillate became neutral. Then the residue was neutralized with aqueous NaOH at pH 8. The residue was diluted with alcohol which resulted in the precipitation of the sodium salt of the title product; yield 30 g.

2. and 3. l-Chloro-2-hydroxy-Z-phosphonopropane and its methyl ester Ref.: C.A. 51, l2878e. 29 g of dimethylphosphite and 24.2 g of chloroacetone were heated together to 120C for 24 hrs. The ester crystallized by cooling. The crude product was recrystallized from 'cyclohexane, In.p. 6365; yield 32 g.

The above ester (25 g) was boiled for 8 hrs in' a mixture of 25 g cone. HCl and 100 ml of H 0. After cooling, the crude acid separated as a reddish oil which crystallized slowly on standing.

4. Dichloromethanephosphonic acid Ref.: Lieb. Ann. 679, 51 (1964). A solution of trisdimethylaminophosphine (16.3 g) in anhydrous ether 100 ml) was added dropwise to 23.8 g of CHCL, in 500 m1 of anh. ether. During the addition, the temperature gradually rose to 45C. The ether was then evaporated and a solution of 25 ml cone. HCl in ml of B 0 was added to the residue. After boiling for 4 hrs, the mixture was distilled and gave 21 g of the title acid, b.p. -115/15 mm.

5. Dimethylacetylphosphonate 6. Diphosphonomethane Ref.: .1. Chem. Soc. 1947, 1465. A mixture of diiodomethane (142.5 g, 0.53 mole) and triethylphosphite 157 g, 0.94 mole) was heated progressively from to C, in the course of 5 hrs, in a flask provided 65 with a reflux condenser having an intermediate outlet tube for collecting volatile distillates.

During the heating operation, 30 g of ethyl iodide were collected. The reaction mixture was thereafter distilled and a fraction, b.p. l120/0.51 mm was separated. This fraction which consisted mainly in tetraethylphosphonomethane was hydrolized by boiling 6 hrs in 350 ml of conc. l-lCl. After elimination of the HCl under reduced pressure, the residue was crystallized in a mixture of acetic acid and water which gave 2.3 g of the title product, m.p. 2036. The product was identified by IR and NMR spectroscopy.

7. and 8. 1,2Diphosphonoethane and corresponding ethyl ester Ref.: .1. Chem. Soc. 1947, 1465. A mixture of triethylphosphite 157 g, 0.94 mole) and ethylene dibromide (100 g, 0.53 mole) was heated progressively to 150C (6 hrs) in the apparatus used for preparing the product of Example 6. During the reaction, 65 g of ethyl bromide were collected. At the end of the heating period, the mixture was temporarily heated to 170C and allowed to cool.

The crude mixture was distilled and gave 666 g of the title product tetraethylester, b.p. 1408/0.51 mm. 40 g of the above ester were hydrolized by boiling with 400 ml conc. HCl for 6 hrs. After evaporation of the HCl, the residue gave, after crystallization, 24 g of the desired acid, m.p. 2071 1. The structure of the compound was confirmed by IR and NMR spectroscopy.

9. 1,3-diphosphonopropane Ref.: J. Chem. Soc. 1947, 1465. (EtO) P(157 g, 0.94 mole) and 1,3-dibromopropane (107.6 g, 0.53 mole) were treated as described above for 5 hrs at 130l 70C. Propyl bromide 59.2 g was eliminated and distillation of the residue gave 56.5 g of tetraethyl 1,3- diphosphonopropane, b.p. 156-165/0.51 mm.

The crude acid (30 g), mp. 149155 was obtained as usual from boiling the above ester for 6 hrs in 600 m1 conc. HCl.

10. Phosphonoacetic acid (Hydroxycarbonylmethane phosphonic acid) Ref.: C.A. 41, 700. Sodium ethoxide (27.2 g, 0.4 mole) was added to a solution of diethylphosphite (55.2 g, 0.4 mole) in 200 ml of anhydrous xylene. While keeping the temperature around 0-10C by cooling, ethyl bromoacetate (66.8 g, 0.4 mole) was added dropwise to the above mixture. The NaBr which formed was centrifugated out and the clear liquid was then distilled which gave diethyl ethoxycarbonylmethanephosphonate, b.p. 8085/1 mm.

4.62 g of the above ester were hydrolized by boilingfor hrs with 100 ml conc. HCl and gave 0.8 g of the title acid, m.p 138-14l. The structure was confirmed by IR and NMR spectroscopy.

1 1 Di-(phosphonomethyl)-ether Ref.: C.A. 1943, 3049. Sodium ethoxide (39.44 g, 0.58 mole) was reacted with 74.8 g (0.58 mole) of diethylphosphite in 250 ml of anhydrous xylene. Then, ml (0.29 mole) of di-(chloromethyl)ether was added slowly under cooling. The mixture was heated 3 hrs to 90C and the NaCl formed was filtered out. Reduced pressure distillation of the clear phase gave 37 g of the tetraethyl ester of the title product.

The above ester was boiled 20 hrs with 300 ml of concentrated HCl. Then, after evaporating the volatile fraction under reduced pressure, the residue was dissolved in ml water, treated with 2 g of active carbon and filtered hot. Then it was neutralized to pH 8 (NaOl-l) and evaporated. The product which crystallized overnight was shown to be the symmetrical diethylesterdisodium salt of the title acid.

12. Tetraethyl 1 ,3-dihydroxyl 1 -diphosphonopropane Ref.: .1. Am. Chem. Soc. 78, 4453 (1956). Diethylphosphite (69 g) was slowly added to B-propiolactone 18 g) in the presence of 4 ml of triethylamine as catalyst. During the addition (one-half hr), the temperature progressively rose to 100C. The mixture was stirred for 4 hrs at room temperature then it was left overnight.

After eliminating the excess of diethylphosphite, distillation gave 26 g of the title product, b.p. l30133/15 mm.

13. Diethyl 2-hydroxyethanephosphonate 14. Diethyl N-butylacetamidophosphonate Ref.: Canadian Patent No. 509.034. Under strong cooling, butyl isocyanate (25 g) was slowly dropped into a solution of sodium (0.4 g) in diethylphosphite (34.5 g), so as to maintain the temperature below 5C. After standing overnight the crystallized product was filtered off; yield 12.5 g, m.p. 3233C.

15. Reaction product of glucose with H PO 45 g of glucose and 20.5 g of orthophosphorus acid were stirred together for 24 hrs at room temperature in 250 ml H O. Thereafter, the water was removed by evaporation and the residue washed with alcohol and dried whereby it slowly crystallized. Yield 51 g.

16. and 17. Diphosphono-dichloromethane and diphosphonocarbonyl (esters and Na salts) Ref.: J. Org. Chem. 32, 41 1 l (1967). Tetraethyl methanediphosphonate (described hereinabove) was chlorinated or brominated either by the action of the corresponding halogen or by means of the correspnding hypohalogenite. The halogen groups were eliminated by mild alkaline hydrolysis for obtaining the carbonyl diester. Sodium salts of the corresponding acids were prepared according to the above reference.

EtO Tl) CH VB i P d 1=\ HO OH OH Ref.: Belgian Patent No. 619.619. The free acid was prepared according to the method described above in the case of the compound of Example 1. with 82 g (1 mole) of H PO and 1 10 g (1.1 mole) of acetic anhydride.

50 g of the pure tetrafunctional acid were boiled for 10 hrs with 500 m1 of ethanol. Elimination of the excess alcohol by evaporation gave an oily colourless residue which was titrated with alkali and showed to be a di-- acid. Analysis confirmed its structure. It was used as such in electroplating baths.

Surprisingly, it was found to be more active as an additive than the corresponding original tetrafunctional acid.

In order to otherwise demonstrate the action of the present organophosphorus additives on sulfite gold and gold alloys electroplating baths. the following experiments were performed.

A bath for the electrodeposition of gold alloys was prepared by dissolving the following ingredients in water In grcdicnts Concentration Au (as sulfitc) 4 g/l Ni (as NiSOroH O) 12 g/l Cd (as CdSO,) 10.6 g/l Cu (as DTPA complex) 0.05 g/l Nat- S0 g/l Citric acid 25 g/l Disodium EDTA'2H. l 15 g/l pH (NaOH or H 80 9.5

0.005 mole/l of some of the above described additives were added to fractions of this bath and the electrolytic polarization curves of the modified baths were measured. These curves represent the correlation between the plating current and the corresponding plating voltage applied betwen standard reference electrodes. The measurements were performed with the following apparatus: WENKING-68TSI potentiostat" GERHARD BANK ELEKTRONIK coupled to a function generator (HEWLETT-PACKARD, Model 3310A) and to a precision XY recorder. The variation of applied voltage was a triangular signal having a frequency of 5 l()"" Hz. This signal was swept over about 2 volt in min. The reference electrode was the saturated calomel electrode. (E 0.2154 i 0.006V at 60C). The baths were stirred and three degrees of agitation were available: weak (3 m/min.), medium (78 m/min.) and strong (202l m/min.). The cathode surface (gilt brass) was 20 cm the anode (platinated titanium) was 60 cm The volume of the solution was 600 ml. The temperature was controlled i O. 1C).

FIGS. 1 to 7 show the results obtained. On each of said FIGS., curve (a) represents the behaviour of the above bath without additives (control); whereas curve (b) expresses the effect of the additive. The position and the shape of these curves indicate that, in general, the effect of the organophosphorus additives is to pro duce a rightwise displacement of the curve and to make it steeper. This trend correlates with a standardization action on the electrodeposition potentials of the various metals of the plated gold alloy. The composition of this alloy was about 18 carat and about 20 Cd.

FIG. I concerns the additive of Example 1 FIG. 2 concerns the additive of Example 5 FIG. 3 concerns the additive of Example 6 FIG. 4 concerns the additive of Example 12 FIG. 5 concerns the additive of Example 13 FIG. 6 concerns the additive of Example 18 FIG. 7 concerns, for comparative purposes, the tetraacid (HO) POC(CH )Ol-IPO(OH) which corresponds to the additive of Example 18.

We claim:

1. In an aqueous electroplating bath for the deposi tion of gold or a gold alloy from a sulfite complex. the improvement comprising including from 1 mg/l up to the solubility limit of, the bath of an ester of an organophosphorus compound of the formula wherein R represents Cl, Br, I, or a free or esterified OH group; R represents H, halogens or C to C linear or branched alkyl or alkenyl groups which may be substituted by a group selected from the group consisting of OH, CN, Cl, Br, 1, COOH, SO H and PO H which can be free. salified or esterified, and carbonyl groups; and wherein the acid functions are at least partially esterified with lower alcohols of l to 6 carbon atoms.

2. The bath of claim 1, wherein the ester functions are derived from the group consisting of the lower halogenated and non halogenated alcohols.

3. The bath of claim 2, wherein said alcohols are selected from the group consisting of CI-I OH, C H Ol-I, C l-LOH, iso-C I-I OH, CJ-I OH, iso-C H OH,

ClCI-1 -CHClOH, and (ClCH. CHOH.

4. The bath of claim 1 wherein the additives are chosen among compounds having the formula Z being an alkyl group having 1 to 6 carbon atoms substituted or not with halogens.

5. A process for obtaining a gold or gold alloy deposit on a conductive surface comprising immersing the surface in the bath of claim 1 and electrolyzing said bath with the surface as cathode.

6. In an aqueous electroplating bath which comprises as the main ingredient for the deposition of gold and gold alloys 0.5 to 30 g/l of gold as sulfite, l to 150 g/l of alkali metal or ammonium sulfite, 0.1 to g/l of chelating agents selected among organic acids and hydroxyacids and dior polyamines free or substituted by acetic groups, 0 to g/l of at least one metal acting as a brightening agent or as an alloying metal with the gold present as a salt or water-soluble chelate, enough acids, bases or buffers for maintaining the bath at an approximately constant pH in the range of pH 5 to l 1 during electrolysis, the improvement comprising in cluding from 1 mg/l up to the solubility limit of the bath of an ester of an organophosphorus compound of the formula (HO) OPCRR" PO(OH) wherein R represents Cl, Br, I, or a free or esterified OH group; R represents, H, halogens or C to C linear or branched alkyl or alkenyl groups which may be substituted by a group selected from the group consisting of OH, CN, Cl, Br, 1, COOH, 80 1-1 and 1 0 1-1 which can be free, salified or esterified, and carbonyl groups; and wherein the acid functions are at least partially esterified with lower alcohols of l to 6 carbon 

1. IN AN AQUEOUS ELECTROPLATING BATH FOR THR DEPOSITION OF GOLD OR A GOLD ALLOY FROM A SULFITE COMPLEX, THE IMPROVEMENT COMPRISING INCLUDING FROM 1 MG/L UP TO THE SOLUBILITY LIMIT OF THE BATH OF AN ESTER OF AN ORGANOPHOSPHORUS COMPOUND OF THE FORMULA
 2. The bath of claim 1, wherein the ester functions are derived from the group consisting of the lower halogenated and non halogenated alcohols.
 3. The bath of claim 2, wherein said alcohols are selected from the group consisting of CH3OH, C2H5OH, C3H7OH, iso-C3H7OH, C4H9OH, iso-C4H9OH, ClCH2OH, Cl2CHOH, Cl3COH, ClCH2-CH2OH, ClCH2-CHClOH, ClCH2-CH2-CH2OH and (ClCH2)2CHOH.
 4. The bath of claim 1 wherein the additives are chosen among compounds having the formula
 5. A process for obtaining a gold or gold alloy deposit on a conductive surface comprising immersing the surface in the bath of claim 1 and electrolyzing said bath with the surface as cathode.
 6. In an aqueous electroplating bath which comprises as the main ingredient for the deposition of gold and gold alloys 0.5 to 30 g/l of gold as sulfite, 1 to 150 g/l of alkali metal or ammonium sulfite, 0.1 to 100 g/l of chelating agents selected among organic acids and hydroxyacids and di- or polyamines free or substituted by acetic groups, 0 to 150 g/l of at least one metal acting as a brightening agent or as an alloying metal with the gold present as a salt or water-soluble chelate, enough acids, bases or buffers for maintaining the bath at an approximately constant pH in the range of pH 5 to 11 during electrolysis, the improvement comprising including from 1 mg/l up to the solubility limit of the bath of an ester of an organophosphorus compound of the formula (HO)2OP-CR''R'''' -PO(OH)2 wherein R'' represents Cl, Br, I, or a free or esterified OH group; R'''' represents, H, halogens or C1 to C6 linear or branched alkyl or alkenyl groups which may be substituted by a group selected from the group consisting of OH, CN, Cl, Br, I, COOH, SO3H and PO3H2 which can be free, salified or esterified, and carbonyl groups; and wherein the acid functions are at least partially esterified with lower alcohols of 1 to 6 carbon atoms. 